Epigenetic mechanisms for silencing glutathione S-transferase m2 expression by hypermethylated specificity protein 1 binding in lung cancer

Cancer. 2011 Jul 15;117(14):3209-21. doi: 10.1002/cncr.25875. Epub 2011 Jan 18.


Background: Glutathione S-transferases M2 (GST-M2) is a detoxifying enzyme. Low expression levels of GST-M2 have been detected in lung cancer cells. However, little is known about the regulation of GST-M2 in lung cancer cells. In this study, the authors investigated the epigenetic regulatory mechanisms of GST-M2 in lung cancer cells.

Methods: The authors evaluated the promoter methylation of GST-M2 in lung cancer cells after treatment with the DNA methyltransferase (DNMT) inhibitor 5'-aza-2'-deoxycytidine (5'-aza-dC). Reporter activity assays, chromatin immunoprecipitation (ChIP), electrophoretic mobility-shift assays, and small interfering RNA (siRNA) assays were used to determine whether the methylation of specificity protein 1 (Sp1) affected binding to the GST-M2 promoter or regulated GST-M2 transcription. Real-time polymerase chain reaction was used to determine GST-M2 and DNMT-3b messenger RNA levels in 73 nonsmall cell lung cancer (NSCLC) tissues.

Results: GST-M2 expression was restored after treatment with 5'-aza-dC in lung cancer cells. GST-M2 exhibited high frequency of promoter hypermethylation in lung cancer cells and NSCLC tumor tissues. CpG hypermethylation abated Sp1 binding to the GST-M2 promoter in lung cancer. Knockdown of Sp1 in normal lung cells reduced GST-M2 expression, and silencing of DNMT-3b increased GST-M2 expression in lung cancer cells. In addition, DNMT-3b expression was significantly higher in lung tumors with low levels of GST-M2 expression than in lung tumors with high levels of GST-M2 expression, especially among women and among patients who had stage I disease.

Conclusions: Epigenetic silencing of GST-M2 was distinguished from Sp1-mediated GST-M2 transcriptional expression. The authors concluded that this represents a mechanism that leads to decreased expression of GST-M2 in lung cancer cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Azacitidine / analogs & derivatives
  • Azacitidine / pharmacology
  • Carcinoma, Non-Small-Cell Lung / genetics*
  • Cell Line, Tumor
  • DNA Methylation*
  • Decitabine
  • Enzyme Inhibitors / pharmacology
  • Epigenesis, Genetic*
  • Female
  • Glutathione Transferase / antagonists & inhibitors
  • Glutathione Transferase / genetics*
  • Humans
  • Lung Neoplasms / genetics*
  • Male
  • Sp1 Transcription Factor / genetics*


  • Enzyme Inhibitors
  • Sp1 Transcription Factor
  • Decitabine
  • Glutathione Transferase
  • glutathione S-transferase Mu 2
  • Azacitidine